Performing tomography on multiphase mixtures is a way to determine properties of the multiphase mixture, where the properties may be measured in a pipeline, conduit, wellbore or other structure carrying flow of a multiphase mixture.
The challenge with multiphase flow measurement is that both the phase distribution and the phase velocity profile vary significantly in time and space, as manifested by various flow regimes (patterns) mapped for different pipe deviations, typically as a function of liquid-liquid or gas-liquid superficial velocities. Process tomography has been conceived to have the potential of measuring dynamic multiphase processes such as multiphase flows of complex regimes through a pipeline or in a process vessel. The basic concept is to mathematically reconstruct, from appropriate multiple measurements made at a pipe/vessel periphery, the phase holdup and/or phase velocity profiles, at a sufficient spatial and temporal resolution.
The term “holdup” denotes the fraction of a particular fluid present in a cross-section of pipe. Because each fluid moves at a different speed due to different gravitational forces and other factors, the holdup of a particular fluid is not the same as the volumetric-flow-rate proportion of the total volumetric flow rate due to that fluid. Individual volumetric flow rate can be derived by integrating phase holdup and phase velocity profiles over the pipe cross-section.
A lot of academic and industrial research efforts have been devoted to imaging multiphase flow phase holdup, based on electrical capacitance tomography (ECT), electrical resistance tomography (ERT), electrical impedance tomography (EIT), electrical magnetic tomography (EMT), and their combinations such as ECT and ERT. Research effort has also been put into other ways of measuring multiphase flow. For some of the electrical tomography sensing techniques, processing of the experimental data has been problematic. For instance US patent application 2010/0213953A1 (relating to a method and apparatus for producing particle density map images of particles in a fluidized bed apparatus by ECT) describes a capacitance measurement normalization model which does not permit the auto-removal of effects of pipe-wall capacitance(s), and furthermore, the images reconstructed on the basis of such normalized capacitances only provide an indirect, qualitative result of flow mixture dielectric constant or permittivity.